Mining, uncertainties with

The Bureau of Mines report states that minor corrections for bends, tees, and even compressibility are unnecessary due to the greater uncertainties in actual line conditions. Their checks with the Weymouth relation omitted these corrections. The relation with pres-... 

Once the pure mineral powders characterized, 3 mixtures were manually prepared and named ML1, ML2 and ML3. They contain each of the 8 minerals in different proportions reproducing 3 mine tailings falling in the uncertainty zone of the static test used. The 3 synthetic tailings were characterized with the same techniques as for the pure minerals. Cp and Sp weight fractions were evaluated from their chemical element tracers (respectively Cu and Zn) obtained from ICP-AES analysis. Qz, Dol, and Sid samples are considered pure and their percentages in the mixtures are not corrected. Table 1 presents the fraction of each mineral in the three mixtures before and after correction taking into consideration the contamination of Po sample by pyrite and calcite, as previously determined. The corrected mineral proportions are used for calculation of the static test parameters based on... 

At a large workshop of about 150 dog people in Ljubljana, Slovenia, some years ago, the case for mine detection dogs (MDDs) was debated. No consensus was reached. There were just too many opinions, stresses, and uncertainties. The work group at the GICHD started basically with the same problems but through the persistence of Havard Bach and others the problems became less. 

The Mixture of Concern Approach This approach can be used only if adequate toxicity data on the specific chemical mixture of concern are available. Having the data means that sufficient and appropriate experimental testing has been done and that the results are on record about this mixture s toxicity. This is the most direct and simplest approach, with the fewest uncertainties to derive a criterion or acceptable level for stable mixtures such as fuel oils, jet fuels, mixtures of polychlorinated biphenyls (PCBs), and polybrominated biphenyls (PBBs) [10]. However, working from available data may leave uncertainties about the precise composition of a mixture undetermined. Very few mixtures other than those mentioned above have been studied adequately for toxicity assessment. Hence this data-mining approach is the least frequently used method. 

Accurate assessment of human health risks associated with oral exposure to metals requires knowledge of the fraction of the dose absorbed into the blood. This information is important for As-contaminated environmental media, such as soil and mine waste, because metal contaminants exist in a variety of soluble and insoluble forms and may be contained within particles of inert matrix, such as rock or slag. Physicochemical properties such as these influence the enteric absorption fraction (bioavailability) of ingested metals. Therefore, site-speciflc data on metal bioavailability in the environmental media of concern will increase the accuracy and decrease the uncertainty in human health risk estimates. 

Blanchard et al. (1969) reported a positive correlation between the log of lead-210 concentration in post-mortem derived bone and the log of estimated miners cumulative exposure. However, more lead-210 was observed in bone than was predicted by the model utilized. Furthermore, a linear correlation was observed between lead-210 levels in blood and that in bone however, for both of these analyses sample numbers were small (n=11 to 22). Another study (Clemente et al. 1984) has analyzed the correlation between lead-210 in human teeth and environmental radon levels in various countries. This analysis reported that for the incremental increase in lead-210 in teeth, a value of 3.24x10 pCi (1.2x10 Bq) radon-222/gm of tissue has been associated with a lifetime exposure to 1 WLM. All of these studies are limited by the difficulty in estimating exposure to individuals on the basis of mine levels and worker histories (often related by next of kin). Such estimates, although unavoidable, introduce considerable uncertainty into these analyses. In addition, lead-210 can be introduced in cigarette smoke, food, and ambient air, thus confounding results of studies (NCRP 1984b). 

In addition to the requirement of using coal with a low sulphur content, there is also the objection to strip mining this material. The undesirability of this also contributes to the uncertainty in the estimates of the true availability of coal. 

Mutually unambiguous correspondence between the number of initial analytes and their derivatives should be assured. The optimal case for all compounds is 1 1, but numerous examples of type 1 2 are known (e.g., the derivatization of enantiomers by chiral reagents, which leads to the formation of a pair of diastereomers). Similarly, the reaction of carbonyl compounds with D-alkoxya-mines gives pairs of syn- and a ri-isomers of oxime D-ethers, etc. All processes that lead to further uncertainty (chemical multiplication of analytical signals), such as I N (N > 3), are not recommended for analytical practice. In connection with this, the number of reaction by-products should be minimal. 

Although there remain some uncertainties about the amounts of uranium mined in the former Soviet Union in the period between 1945 and 1990, it is nevertheless now possible to produce a rough picture of cumulative world production since fhe end of World War II. Table 10.2 summarizes historical production, with estimates of production in countries where data are not fully available. 

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